The present invention relates generally to an electronically controlled mechanical timepiece which is operated using mechanical energy generated when a mainspring is released as a drive source and, in particular, to an improvement in the generator of the timepiece which converts mechanical energy into electrical energy and uses the output electrical energy to control power generation.
Generally, the principle utilized for driving an electronically controlled mechanical timepiece involves a generator connected to a train wheel. The train wheel is driven using a mainspring as an energy source. The generator generates power by receiving rotation from the train wheel. The speed at which the generator operates is controlled by a mechanical speed control mechanism such as a timed annular balance and escape wheel. However, it is known that the generator can be utilized in place of a mechanical speed control mechanism composed of a timed annular balance and an escape wheel which are inherent to the mechanical timepiece.
An electronic control circuit can be used to control the speed and is driven by the power generated by the generator. The rotation cycle of the generator is controlled in response to a control signal from the electronic circuit. The speed of the train wheel is controlled by applying a brake to the train wheel. Consequently, a battery acting as a drive source of the electronic circuit is not necessary in this structure. Furthermore, a pinpoint accuracy, similar to that of a battery-driven electronic clock, can be obtained.
Unexamined Japanese Patent Publication No. 8-5758 discloses as prior art this type of hybrid type timepiece which was previously developed by the applicant. Reference is made to FIG. 16 in which an example of such a prior art electronically controlled mechanical timepiece is shown. Reference is made to FIG. 17 which depicts an exploded perspective view of a generator 20 used in the timepiece of FIG. 16.
The prior art electronically controlled mechanical timepiece includes a movement barrel 1 composed of a mainspring, a barrel gear, a barrel arbor and a barrel lid. The mainspring has an external end fixed to the barrel gear and an internal end fixed to the barrel arbor. The barrel arbor is supported by a main plate and a train wheel bridge and is fixed by a ratchet wheel screw 5 so that it is rotated integrally with a ratchet wheel 4. Ratchet wheel 4 is meshed with a pawl 6 so that it rotates clockwise and is prevented from rotating in a counterclockwise direction.
The rotational speed, (i.e. the power) from movement barrel 1 containing the mainspring is increased through the train wheel which composed of a second wheel 7, a third wheel 8, a fourth wheel 9, a fifth wheel 10 and a sixth wheel 11. The resultant rotational power is supplied to generator 20.
Generator 20 has a structure similar to a step motor for driving a conventional battery-drive-type electronic clock. Generator 20 is composed of a rotor 12, a stator 15 and a coil block 16.
Rotor 12 is composed of a rotor pinion 12a, a rotor magnet 12b and a rotor inertia disc 12c. Rotor magnet 12b and rotor inertia disc 12c are integrally attached around rotor pinion 12a. Rotor pinion 12a is rotated by being connected to sixth wheel 11.
A stator coil 15a is wound around the periphery of stator 15. Stator 15 has a stator hole 15b at an extreme end of stator 15 for rotatably accommodating rotor magnet 12b. A pair of external notches 15c are formed in stator 15. External notches 15c are formed at intervals of 180.degree. around the periphery of stator hole 15b and are located at the top and bottom tip of stator hole 15b. External notches 15c are recessed toward stator hole 15b. The opposite end of the stator 15 is fixed to a main plate not shown by a screw 21.
Coil block 16 is composed of a magnetic core 16a and a coil 16b. Coil 16b is wound around magnetic core 16a. Both the ends of coil block 16 overlap both the ends of stator 15 when mounted to the main plate and are tightened together by a pair of screws 21 and integrally fixed to the main plate. Stator 15 and magnetic core 16a are made of a PC Permalloy material. Stator coil 15a is connected in series to coil 16b to provide an output voltage obtained by adding the voltages generated by stator coil 15a and coil 16b.
Generator 20 supplies the power obtained by the rotation of rotor 12 to an electronic circuit having a crystal oscillator through a capacitor (not shown). The electronic circuit detects the number of rotations of rotor 12 and supplies a rotor rotation control signal to the coils in accordance with a reference frequency to brake the generator. As a result, the train wheel is rotated at a constant rotational speed at all times in accordance with a braking force applied thereto. However, generator 20 having the above described structure has a problem in its structure and a problem in electromagnetic characteristics.
Generator 20 follows the structure of the conventional step motor. Generator 20 is additionally provided with coil block 16 in order to advantageously generate power while avoiding scramble for other parts such as the train wheel and the like, that is, in order to increase the number of turns of the coil as much as possible.
As a result, stator hole 15b is formed to have a cantilever support structure as shown in the FIG. 16. This structure causes an electromagnetic problem which is not seen in the conventional step motor.
First, since stator hole 15b is formed integrally with stator 15 by stamping or the like, a flux passes through external notches 15c. When rotor magnet 12b of rotor 12 passes external notches 15c, the fluxes of the coils do not change although the fluxes of external notches 15c change. Consequently, a voltage generated is dropped at the positions where rotor magnet 12b passes.
As a countermeasure for preventing the above problem, the width of the external notches 15c is sufficiently reduced in a manufacturing process to thereby decrease an amount of drop in the voltage.
However, when this countermeasure is employed, stator hole 15b is liable to be deformed even by a slight amount of external force applied thereto while it is processed or in a following process such as winding, annealing and the like. Accordingly, performance is varied by the change of the diameter of the stator hole 15b or the deformation thereof and cogging torque is increased, the reby decreasing the efficiency as a generator.
A simple method of detecting the number of rotations of a rotor is to detect the waveform of generated power and convert it to a binary value. However, since the generated voltage is actually dropped at the notch passing-through positions as described above, the waveform is made to a complex mountain-shaped waveform as shown in FIG. 18(b) and therefore it is difficult to detect the waveform.
Further, a finished product is finally attached to the main plate by screws in combination with coil block 16. However, since the coils are heavy, the portion of stator 15 located on the opposite side from external notches 15c is liable to be bent or deformed easily even if a very slight force is applied thereto and therefore careful caution is required in the handling of stator 15. A resultant product which has been deformed as described above is disposed of as a defective product in an inspection process. This leads to a reduction of yields which cannot be avoided in respective processes from the structure of the product.
The present inventions is directed at overcoming inadequacies in the prior art.
An object of the present invention is to provide an improved electronically controlled mechanical timepiece which can solve a problem in handling and improve yields as well as increase a generated voltage at the same time by dividing a stator hole into two sections and easily detect a number of rotations by making the waveform of the generated power to a sine wave.